The diagnosis and treatment of patients with cancerous tumors, premalignant conditions, and other disorders has long been an area of intense investigation. Non-invasive methods for examining tissue include palpation, X-ray, magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging. When a physician suspects that tissue may contain cancerous cells, a biopsy may be done using either an open procedure or a percutaneous procedure. For an open procedure, a scalpel is used to create a large incision in the tissue to provide direct viewing and access to the tissue mass of interest. The entire mass (excisional biopsy) or a part of the mass (incisional biopsy) may then be removed. In most percutaneous biopsy procedures, a needle-like instrument is inserted through a very small incision to access the tissue mass of interest and obtain a tissue sample for later examination and analysis.
Aspiration and core sampling are two percutaneous methods for obtaining a portion of tissue from within the body. In an aspiration procedure, tissue is fragmented into pieces and drawn through a fine needle in a fluid medium. The method is less intrusive than most other sampling techniques, however, it has limited application since the structure of tissue excised by aspiration is destroyed leaving only individual cells for analysis (cytology) and not the tissue structure for analysis (pathology). In core biopsy, a core or fragment of tissue is obtained in a manner, which preserves both the cells and the structure for histological examination. The type of biopsy used depends mainly on various factors, and no single procedure is ideal for all cases. Core biopsy, however, is very useful in a number of conditions and is widely used by physicians.
Examples of core sampling biopsy instruments are described in U.S. Pat. Nos. 5,562,822 and 5,769,086 (both issued to Ritchart, et al), and in U.S. patent application Ser. No. 09/107,845 filed on Jun. 30, 1998. Another example of a core sampling biopsy instrument is the biopsy instrument now marketed by Ethicon Endo-Surgery, Inc., Cincinnati, Ohio, under the trade name MAMMOTOME. Each of these instruments is a type of image-guided, percutaneous, coring, breast biopsy instrument, which uses a vacuum for retrieving tissue samples. A physician uses these instruments to capture "actively" (using the vacuum) tissue prior to severing it from the body. In particular, in these biopsy instruments, tissue is drawn into a port at the distal end of a piercing element, hereinafter referred to as a piercer. A cutting element, hereinafter referred to as a cutter, is rotated and advanced through a lumen of the piercer past the port. As the cutter advances through the port, it severs the tissue drawn into the port from the surrounding tissue. While the cutter is generally rotated using some type of motor, it may be advanced either manually or automatically. In the MAMMOTOME instrument, the surgeon manually moves the cutter back and forth by lateral movement of a knob mounted on the outside of the instrument. Once the cutter is in place, proximal to the tissue port, further lateral movement of the knob is prevented and the cutter is advanced through the tissue port to sever tissue by twisting the knob. This arrangement is advantageous because the surgeon is able, through tactile and/or audible feedback, to determine whether the cutter is effectively cutting tissue or if there is a problem, such as binding or stalling. The surgeon may then adjust the speed at which the cutter is moved through the tissue, stop the cutter or back the cutter away from the tissue.
As described in U.S. Pat. Nos. 5,562,822 and 5,769,086, the translation of the cutter may be automated to facilitate the procedure. However, if the procedure is automated as described in those references, the surgeon loses the benefit of the tactile feedback, which results when the cutter is advanced manually. It is generally desirable to ensure that the rotational speed of the cutter does not drop below a predetermined speed in order to sever cleanly the tissue sample from surrounding tissue and to avoid damage to the tissue sample. Automating translation of the cutter will, to some extent, eliminate the tactile feedback that the surgeon gets from moving the cutter manually. The advantageous method of automatically measuring and controlling the rotation and translation of the cutter is not described for either of the devices in the '822 or '086 patents. This automatic control method could be used, for example, to prevent the cutter from advancing when the opening is blocked by something other than tissue. Such an automatic control method could also be used to ensure that the cutter rotates at an optimal speed to ensure proper cutting of the tissue and to prevent the cutter rotational speed from dropping below a predetermined limit.
Another advantage of a core sampling biopsy device being used with an automatic control method is that the operator would be able to perform the surgical procedure in less time than with a motorized device having no automatic control method. Since core sampling biopsy devices extract tissue samples from deep within the body of the surgical patient, the penetrating element, or piercer, for accessing the tissue, is necessarily long. The driven element, or cutter, must translate from the proximal end of the piercer to the distal end in order to collect the tissue sample. Then the cutter transports the tissue sample from the distal end of the piercer to the proximal end, which is outside the body of the patient. As the cutter is actually cutting through tissue and collecting the tissue sample, the translational speed of the cutter should be maintained in an optimal range. But for all other portions of cutter translation, the translational speed of the cutter may be relatively high without detrimental effects. Thus the time required for obtaining each tissue sample might be reduced. Since many tissue samples may be extracted from the patient during a typical surgical procedure, the accumulated time saved could be significant, providing obvious benefit for both the surgeon and the patient.
A core sampling, surgical instrument with a needle guiding stage of a stereotactic mammography biopsy system is disclosed in U.S. Pat. No. 5,830,219 by Bird, et al. In this instrument, the driven element (hereinafter referred to as a cutter) translates to cut tissue captured in the distal end of the instrument. This instrument couples feedback from an optical encoder with a microprocessor to calculate cutting resistance so that if the cutter encounters, for example, a dense tissue mass causing the cutter rotation to decrease, additional electrical current is automatically provided to the cutter motor to resume the desired cutter rotational speed. The encoder also provides information to the microprocessor to control automatically the angular stroke of the cutter as it oscillates between the clockwise and counterclockwise directions. This closed loop cutter control method is described in '219 as being provided only for when the cutter is in the cutting portion of its axial travel.
An alternate control method, however, to deal with an increase in cutting resistance (due to encountering dense tissue or obstructions) is to slow incrementally the translational speed of the cutter until a desired cutter rotational speed is resumed. If the cutter cannot penetrate the obstruction and the desired rotational speed cannot be resumed despite reducing translational speed, then the translation of the cutter could be completely halted and an error message, for example, could be transmitted to the operator. This alternate control method would have an advantage of preventing damage to the biopsy instrument because the tissue sample is obtained less aggressively due to the slowed advance of the cutter through the tissue, or else the cutter translation is completely halted if the obstruction is impenetrable.
Another advantage for reducing the cutter translational speed rather than increasing the cutter rotational speed in response to an increase in rotational resistance on the cutter is that smaller, less powerful, and less expensive motors could be used to drive the cutter. Both the translation motor for advancing the cutter and the rotation motor for rotating the cutter may be smaller because the overall rate at which work would be done on the tissue by the cutter could be reduced. Using smaller, lighter weight motors would also facilitate their incorporation into the handheld portion of the biopsy instrument. As described in pending U.S. patent application Ser. No. 09/178,075, the motors can be remotely located in a separate control unit and operationally connected to the handheld portion of the biopsy instrument by at least one rotatable shaft. In such a biopsy instrument, using small motors would be advantageous in allowing the use of small diameter, lightweight, rotatable shafts. In addition to the cost savings realized in the manufacture of the device, the biopsy instrument could be more hand manipulatable by the operator during the surgical biopsy procedure.
It is also advantageous to use both types of responses to increased rotational resistance on the cutter. That is, a single control method that combines a method for decreasing cutter translational speed and a method for increasing cutter rotational speed in response to decreasing cutter rotation may be used. For example, if the cutter encounters an obstruction in tissue and the cutting resistance rises sharply, the electrical current to the cutter rotational motor may automatically be increased by a predetermined amount. If the cutter rotational speed is measured and compared to a desired, predetermined cutter rotation speed, and it is determined that the cutter rotational speed is still not high enough, than the cutter translational speed may be decreased by a predetermined amount. These steps could be repeated automatically until the tissue sample is obtained, or until certain operational thresholds (minimal translation speed, maximum current to rotation motor, for example) are reached. By using such a combined method in response to increasing rotational resistance on the cutter, the cutter rotational and translational motors may be smaller than when using a method to modify cutter rotation alone.
When an operator uses a handheld instrument operationally connected to a remotely located motor by a flexible, rotatable shaft, the operational configuration of the rotatable shaft may affect the efficiency of the mechanical energy transmitted to the handpiece. For example, if it is necessary for the operator to hold the handheld instrument during the surgical procedure so that the flexible, rotatable shaft is sharply curved, the resistance to rotation of the rotatable shaft is higher than if the rotatable shaft was in a straight configuration. Also, when the operator manipulates the probe of the instrument to penetrate into the tissue mass of interest, a bending moment may be unavoidably applied to the piercer of the probe, increasing the rotational resistance of the cutter which is constructed coaxially in close alignment with the piercer. There also may be additional mechanical losses, for example, due to wear or misalignment of power transmission components. Therefore, it would be advantageous to be able to measure the total, rotational resistance before the cutter encounters tissue, so that the cutter rotation may be increased to the desired, predetermined rotational speed for cutting tissue.
For an automated, handheld biopsy device, the cutter rotation and translation motors may be mounted in a remote unit in order to minimize the overall size and weight of the handpiece. As described in U.S. patent application Ser. No. 09/178,075, each motor may be operationally connected with the cutter of the handpiece of the biopsy device by a flexible, rotatable shaft. A tradeoff associated with using a flexible, rotatable shaft is that the shaft may twist along its length, or "wind" under loading. A measurement on the proximal end of the rotatable shaft of the angular position of the shaft may vary from that on the distal end. Since the precise number of shaft rotations may be used to calculate axial position of the cutter, it is desirable to incorporate a high-resolution means within the biopsy device to measure and compensate for the twisting of the flexible, rotatable shaft operationally connected to the remotely located translation motor.
What is needed is a core sampling biopsy device having a control method and apparatus that allows the cutter translational speed to be automatically responsive to cutting resistance caused by obstructions or dense tissue encountered by the cutter. What is further needed is a core sampling biopsy device having a control method and apparatus that allows the cutter rotational speed to be automatically responsive to total rotational resistance on the cutter before and during the cutting of tissue. What is further needed is a core sampling biopsy device having a control method and apparatus that allows the cutter translational speed to be automatically responsive to cutter translational position so that surgical procedure time may be reduced. What is finally needed is a high-resolution means within the biopsy device to measure and compensate for the twisting of the flexible, rotatable shaft operationally connected to the remotely located translation motor.